Considerable work has been directed toward the development of seat assemblies or chairs which are ergonomically well suited for use by persons who are engaged in tasks that require that they be seated for prolonged periods of time. Typical of such applications are the seats or chairs which are used in offices or at home for tasks such as typing, reading and computer use.
In recent years it has been recognized that it is highly desirable for such seat assemblies or chairs to be constructed in a manner which allows the seat to move along an upwardly concaved arcuate path, or some approximation thereof. Such arcuate movement is most desirably implemented by mounting the seat for movement about an arcuate path having a center of curvature which is proximate the center of mass of the person seated on the seat. This geometry dynamically balances the bio-mechanics of a user's body with movement of the chair so that the user can have a plurality of equilibrium positions in a variety of postures. The design principle is one of counterbalanced motion in which the mass of the user's body is counterbalanced by angular forces of the motion of the seat in a fore-and-aft direction.
My previous U.S. Pat. Nos. 5,244,252; 5,460,427; 5,558,399 and 5,735,574 describe in more detail the advantages of mounting a seat for movement along an upwardly concaved path having a center of curvature proximate the center of mass of the person seated on the seat. These patents are incorporated herein by reference. Such seat assemblies also are particularly well suited for use in vehicles in order to dissipate the dynamic forces generated when the vehicle is involved in a sudden deceleration or crash.
In addition to mounting the seat of a chair for arcuate movement, it is also well known to mount the back of the seat assembly for movement or for movement of a portion of the back, such as the lumbar support region. Various schemes for moving the back are also disclosed in my above-referenced patents. Most of these movable back mounting systems couple the back to the seat and have been designed primarily for dynamic deceleration in vehicles, but they are usable to varying degrees in office chairs.
U.S. Pat. Nos. 5,261,732; 5,366,269; 5,437,494; 5,577,802; 5,961,073; 5,979,984 and 6,334,648 disclose chairs or seat assemblies in which one or both of the back and seat are mounted for movement. It is also well known in office chairs and the like to provide for backrest reclining mechanisms as, for example, are shown in U.S. Pat. Nos. 5,975,634 and 6,086,153.
Generally, however, there still remains a need for a chair or seating assembly which can be used for long periods of time that has a movably mounted seat and backrest which will accommodate a wide range of seating postures while providing many balanced or equilibrium positions matched to the bio-mechanics of the user's body. Thus, the person using the chair will want to assume various postures, such as a forward reaching posture (where the person is performing manual tasks on a support surface such as a desk), or an erect posture (for tasks such as typing), or a semi-reclined posture for increased comfort. The seat and backrest should be movable to an equilibrium position about which dynamic micro-adjustments of the user's body and the seat assembly about the center of mass of the user are possible in order to provide the greatest comfort during prolonged use.